Eagle, Bald

Haliaeetus leucocephalus

Adults have a brown-black body and a white head and tail. The wings are long and broad, the tail squared and the legs are yellow. Juvenile eagles are chocolate brown, but with mottled white on their tails, bellies and wing linings. It is not until their fourth year that the birds acquire the white head and tail feathers identifying them as adults. Not until their sixth year do they lose all their immature plumage. Female body length varies from 35 to 37 inches, slightly larger than the male, with a wingspan that varies from 79 to 90 inches. Male body length varies from 30 to 34 inches. Their wingspan ranges from 72 to 85 inches. Weight varies from ten to fourteen pounds. Northern birds are significantly larger than their southern relatives.

Family

Accipitridae

Order

Falconiformes

Class

Aves

Range

North America from Alaska to California and Florida, absent from the northernmost region of Canada.

Habitat

Lakes, seacoasts, reservoirs, rivers, and inland waters, highest of treetops, rocky hillsides, cliffs, and peaks.In the wild, 20 - 30 years, and up to 50 years in captivity.

Life Expectancy

In the wild, 20 - 30 years, and up to 50 years in captivity.

Sexual Maturity

Approximately 5 years.

Diet

In the wild, they eat fish, birds, snakes, and carrion. In the Zoo, they are fed Bird of Prey diet, chicks, smelt, whiting, rats, and horse knucklebones.

Status

IUCN - Least Concern

Behaviors

Bald eagles are diurnal (active during the day). They are efficient, versatile, opportunistic hunters who will often steal the prey of other raptors. While flying, they have a cruising speed of between 30-40 mph and can dive at a rate of approximately 100-mph. Members of the fish eagles, bald eagles in the northern parts of their range migrate far enough south to winter along unfrozen bodies of water where they can continue to hunt. In the spring, bald eagles are common migrants to the White, Green, Catskills, and Allegheny Mountains. Bald eagle nests are thought to be the largest of all birds, reaching 11 feet deep, 6 feet wide and weighing from several hundred pounds to as much as a ton! Breeding pairs return to their nest each year, adding materials and repairing them. Once paired, bald eagles remain together until one dies. The survivor will take a new mate. Clutch size is two buff-white eggs, and incubation lasts 34 to 35 days. The young fledge at 10 - 11 weeks and may return on occasion after that.

Adaptions

Bald eagles have 7,000 feathers, lightweight yet extremely strong and hollow yet highly flexible. Feathers protect the bird from the cold as well as the heat of the sun, by trapping layers of air. To maintain its body temperature an eagle simply changes the position of its feathers. Feathers provide waterproofing, protection, and are crucial for flight. The tail of the bald eagle is very important for flight and maneuvering. While the bald eagle is soaring or gliding, the tail feathers are spread in order to attain the largest surface area and increase the effect of thermals and updrafts. The tail also helps to brake the eagle when landing and assists in stabilization during a controlled dive or when swooping toward prey. Talons are important tools for hunting and defense. Eagles kill their prey by penetrating the flesh with their talons. The hook at the tip of the beak is used for tearing. The upper mandible has an edge sharp enough to slice tough skin. The mandible overlaps the lower, creating a scissors effect. A bald eagle’s beak is a strong weapon, but is also delicate enough to groom a mate’s feathers or feed a small portion of food to a newly hatched chick. Beak and talons grow continuously. Both are made of keratin, the same substance as our hair and fingernails. The beak of a captive eagle is not worn down naturally, so it must be trimmed annually. Bald eagles have very keen eyesight. They have two centers of focus that allow the birds to see both forward and to the side at the same time. Bald eagles are capable of seeing fish in the water from several hundred feet above, while soaring, gliding, or in flapping flight. Their eyesight is estimated to be eight times better than our own. Eagles have eyelids that close during sleep. For blinking, they also have an inner eyelid called a nictitating membrane. Every three or four seconds, the nictitating membrane slides across the eye from front to back, wiping dirt and dust from the cornea. Because the membrane is translucent, the eagle can see even while it is over the eye.

Special Interests

The bald eagle’s scientific name signifies a sea (halo) eagle (aeetos) with a white (leukos) head. Possession of a feather or other body part is a felony with a fine of up to $10,000 and/or 10 years in prison. Native Americans are able to possess these parts, by permit, to continue in the practice of their culture and religion. Bald eagles may use the same nest year after year; adding more twigs and branches each time. One historic nest spanned 86 square feet on top and contained “two wagon loads” of material. Another nest was 10 feet across and 16.5 feet high. A bald eagle’s plumage weighs approximately 17% of the bird’s body mass. The skeleton only weighs 7% of its body mass. In 1782, Charles Thompson, Secretary of the Continental Congress, designated the bald eagle as the symbol of the fledgling United States. Among the members of Congress who opposed the idea was Benjamin Franklin who did so on the grounds that the bald eagle was a “bird of bad moral character.” Benjamin Franklin proposed the wild turkey as our symbol, but we all know who won that argument. In the emblem, the eagle has olive branches in its right claw as a symbol of peace, and a bundle of arrows in its left claw as a symbol of unity.

Folklore

The bald eagle is not bald; it actually has white feathers on its head, neck, and tail. Bald is a derivation of “balde”, an Old English word meaning white. The eagle was named for its white feathers instead of a lack of feathers. Bald eagles can actually swim! They use an overhand movement of the wings that is very much like the butterfly stroke.

Conservation

Law enforcement, increased public awareness, restricted/banned use of certain pesticides, and release programs are all part of the bald eagle conservation effort. Habitat destruction, pollution, timber harvesting, and pesticides effect populations. The bald eagle has no known natural enemies. The nationwide decline of bald eagles that took place from the 1940s into the early 1970s was a result of contaminant buildup in the environment related directly to the agricultural and industrial use of pesticides and chemicals. The use of organochlorine pesticides has contributed to reduced numbers of many of the birds of prey. These chemicals have three main properties that effect raptor populations: Organochlorine pesticides are chemically extremely stable, persisting in the environment unchanged for many years. They dissolve fat, which accumulates in an animal’s body and is then passed on from prey to predator. The members of the food chain are particularly susceptible to accumulating large amounts of these toxins. At sub-lethal levels of only a few parts per million in tissues, organochlorines can disrupt breeding resulting in a reduced numbered of young produced per season. In addition, these chemicals can be distributed over a wide area far removed from the initial contamination site by river and air currents, and in the bodies of migrating animals. ALL BIRD SPECIES STUDIED HAVE BEEN FOUND TO BE SUSCEPTIBLE TO THESE PESTICIDES. DDT, one of the first and most well-known organochlorine pesticides, is itself not particularly toxic to birds. Its principle breakdown product, DDE, causes the thinning of eggshells. Such shells often break during incubation. DDE and other breakdown products may also be responsible for embryo deaths in intact eggs. If enough offspring are not produced to offset the natural adult mortality rate, the population declines and the species eventually becomes extinct.

Jacksonville Zoo History

Records indicate that the bald eagle was in our collection as early as 1956.